The cytotoxicity of diffusable miracidial secretions, referred to herein as schistosomal oval cytotoxins (SOC), have been noted by numerous investigators studying Schistosoma spp: eggs in tissues, but they have not been extensively studied. Recently, schistosome egg-related hepatocyte damage has been dramatically demonstrated and described in T-cell deficient nude mice (Byram and Lichtenberg, 1977). The purpose of this study is to develop an in vitro model, taking advantage of currently established techniques, to study and characterize the effects of SOC on primary cultures of rat hepatocytes, embryonic mouse liver cells and fibroblasts. Intact eggs containing mature viable miracidia, immature eggs and various fractions of eggs (miracidial hatching fluid, soluble egg antigen, and egg conditioned media) will be added to cell cultures. S. mansoni, S. japonicum, and S. haematobium eggs will be evaluated and compared. Evaluation of the effects of these treatments will include tests for cell viability and cell injury, ability of liver cells to metabolize drugs, and ultrastructural studies. The proposed studies will clarify the cytotoxic potential of the schistosome egg, may explain some of the differences in the pathophysiology of the 3 species of Schistosoma infecting man and establish a model wherein intrinsic characteristics of parasite ova may be separated from host response.